To manufacture laminated ceramic electronic components such as laminated ceramic capacitors, a process is carried out for applying a conductive paste, which will serve as a conductor film such as an internal electrode, onto a ceramic green sheet, for example. Gravure printing is applied in this process, for example.
When printing a conductor film using a conductive paste, it is necessary to apply fine metal particles serving as a conductive material in a uniform manner and with a certain thickness. As such, compared to color printing of printed materials, film materials for wrapping, and the like, a larger printed film thickness is required, and there is demand for the conductor film to be highly smooth while at the same time ensuring the required paste film thickness.
For example, Japanese Unexamined Patent Application Publication No. 2012-56143 discloses a gravure printing plate including an intermediate step portion, provided in each of cells, that is lower than a first bank and a second bank but is higher than a deep portion, toward the front of a printing direction. Providing the intermediate step portion in this manner reduces variations in the depth dimension near the banks. This in turn reduces a drop in pressure, which suppresses transfer unevenness and by extension increases the smoothness of the surface of a paste film.
However, although the method disclosed in Japanese Unexamined Patent Application Publication No. 2012-56143 does of course increase the smoothness, the method also causes the volume of the cells to drop in the vicinity of the banks, which reduces the thickness of the paste film. Meanwhile, the transferability will worsen in the central areas of the cells, causing a drop in the paste film thickness. There are thus cases where the required thickness cannot be ensured in the printed paste film.
To illustrate the aforementioned poor transferability of the printing paste in the central areas of the cells in particular, the behavior of the printing paste with which the cells are filled when the paste is transferred onto a printing target material during gravure printing will be described with reference to FIGS. 18 to 21. FIGS. 18 to 21 illustrate cross-sectional views of a gravure printing plate 4, having an image section 3, in which banks 1 and cells 2 defined by the banks 1 are provided. This gravure printing plate 4 transfers a conductive paste film 7 onto a ceramic green sheet 6 that is backed by a carrier film 5, serving as a printing target material.
First, as shown in FIG. 18, the cells 2 are filled with a conductive paste 8 serving as a printing paste.
Next, as shown in FIG. 19, the ceramic green sheet 6 that is backed by the carrier film 5 is placed into contact with the image section 3 of the gravure printing plate 4. At this time, the conductive paste 8 adheres to the ceramic green sheet 6 while flowing in the directions indicated by arrows 9. Small air pockets 10 are formed in the conductive paste 8 as well.
Thereafter, the ceramic green sheet 6 is separated from the gravure printing plate 4. FIG. 20 illustrates a state when the ceramic green sheet 6 begins to separate from the gravure printing plate 4. As shown in FIG. 20, the conductive paste 8 begins to be transferred onto the ceramic green sheet 6 from the banks 1 while flowing along the banks 1 in the directions indicated by arrows 11.
Next, FIG. 21 illustrates a state when the ceramic green sheet 6 is further separated from the gravure printing plate 4 and the transfer of the conductive paste 8 has ended. As shown in FIG. 21, the conductive paste film 7 is formed on the ceramic green sheet 6.
The conductive paste 8 inevitably remains in the central areas of the cells 2, as can be seen in FIG. 21. Meanwhile, with respect to the conductive paste film 7 on the ceramic green sheet 6, surface tension acting in the conductive paste itself causes the conductive paste to flow in the direction of arrows 12 after the conductive paste has been transferred starting from the banks 1, and the conductive paste attempts to take on a uniform thickness. However, the conductive paste is thicker than other printing pastes, and there is thus a limit on how uniform the thickness of the conductive paste film 7 can become. As a result, the conductive paste film 7 tends to be thicker in areas corresponding to the banks 1 and thinner in areas corresponding to the centers of the cells 2.
The aforementioned phenomenon in which the transferability is poor in the centers of the cells 2 is caused by the conductive paste 8 remaining in the centers of the cells 2, as well as the difficulty in correcting non-uniform thicknesses in the conductive paste film 7 caused by the transfer of the conductive paste 8 starting from the banks 1, as described above.
The following can be considered as methods for increasing the film thickness in the centers of the cells.
(1) A method that increases the volume of the printing paste with which each cell is filled by making the cells deeper can be considered. However, deepening the cells reduces the accuracy in which the cell shapes are formed. Furthermore, deepening the cells will only increase the amount of printing paste that remains in the bases of the cells and is not transferred, and thus there will often not be enough printing paste to ensure the required film thickness.
(2) A method that increases the volume of the printing paste with which each cell is filled by widening the area of the cell openings can be considered. However, because the transfer of the printing paste starts from the banks, it is easier for the paste film to become thinner as the cell progresses further from the banks, which can result in the smoothness worsening.
In this manner, it is not particularly easy to form a paste film that is both smooth and has the necessary film thickness through gravure printing.